Direct drive generator and wind turbine

ABSTRACT

The invention concerns a direct drive or directly driven generator for a wind turbine comprising a stator having at least one stator element for power generation and a rotor pivotable around a centre axis of the generator having at least one rotor element for power generation, the generator having an air gap between the stator element and rotor element, wherein the stator comprises a front and a rear ring-shaped supporting element and stator segments being attached to the front and rear ring-shaped supporting elements of the stator, wherein junctions between the front and rear ring-shaped supporting elements of the stator and stator segments are located substantially at a radius in relation to the centre axis of the generator which is smaller than the radius of the air gap between the stator element and rotor element. Furthermore the invention concerns a wind turbine comprising such a direct drive generator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European application No. 07022882.0filed Nov. 26, 2007, which is incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The invention relates to a direct drive or directly driven generator aswell as to a wind turbine comprising a direct drive generator.

BACKGROUND OF THE INVENTION

In principle there are two main types of wind turbines in view of thedrive configuration of a wind turbine. The first type of a wind turbineis the more classical type of a wind turbine comprising a gearboxarranged between a main shaft and a generator of the wind turbine. Thesecond type of a wind turbine is a gearless type, whereat the gearboxand the conventional generator are substituted by a multipolargenerator, a so called direct drive or directly driven generator. Such adirect drive generator can be made as a synchronous generator withwinded rotor or with permanent magnets attached to the rotor, or it canbe designed as an alternative type of a generator.

Common to direct driven generators is that their physical dimensions arerelatively large. At a typical air gap diameter of approximately 5 m fora multi-megawatt direct drive generator the outer diameter is on theorder of approximately 6 m or even more. The large outer diameter makesthe transport of the direct drive generator difficultly and the heavydead load of the direct drive generator involves further difficultiese.g. concerning the replacement for repair by occurred breakdowns.

A further difficulty arises in the normal configuration of a windturbine with a direct drive generator, where the direct drive generatoris arranged between the wind turbine rotor and the tower in order toyield a compact machine construction. In this case it will be necessaryto dismantle the whole wind turbine rotor by a required dismantling ofthe direct drive generator.

To overcome these problems at least partially there were somesuggestions to divide parts of the generator.

In WO 98/20595 A1 a stator for a rotating electric machine is disclosedcomprising a stator core and a winding. The stator core is provided withstator teeth extending radially inwards towards a rotor. Each statortooth is configured as a number of tooth sections joined axially into astator tooth plank. That stator tooth planks are fitted together side byside thus forming a section of the stator core. This construction makesthe transport of parts of the rotating electric machine to the site oferection partially easier, because the stator can be assembled on site.However, this construction requires a stator housing as such havingrelatively large outer dimensions.

From U.S. Pat. No. 4,594,552 an armature winding of a split stator isknown. The split stator has a slotted core divided by at least twocircumferentially-spaced split lines to facilitate the assembly and thedisassembly of the split stator. The armature winding comprises armaturecoils in the slots of the stator core connected to provide poles andarranged to provide a plurality of armature coils divided at the splitlines. Connecting and disconnecting means are provided to connect anddisconnect the armature coils when the split stator is assembled anddisassembled, respectively. This construction, however, also requires astator housing as such having relatively large outer dimensions.

U.S. Pat. No. 5,844,341 describes an electric generator to be driven bya low speed device such as wind turbine. The generator consists of oneor more rotor rings of many permanent magnets of alternating polarityand coaxial stator rings of many laminated yokes, each yoke definingslots to locate coils. The yokes and coils form modules which aresupported by beams relatively to the rotor rings. The drawback of thisconfiguration is that the electromechanical properties in this form ofmodular construction with single polar pairs separated by air gaps maybe disadvantageous, and that a possible dismantling of a single statormodule can involve that the whole generator has to be opened in situimplying risk of humidity, dirt etc., and that it may be cumbersome ifthe stator module has to be taken out in a disadvantageous direction.

U.S. Pat. No. 6,781,276 B1 describes a generator for a wind turbinecomprising a stator and a rotor. The stator has a number of statormodules that are individual and which may be installed, repaired anddismantled individually and independently of each other. This generatorhas no part larger than the air gap diameter. But even if no part islarger than the air gap diameter, the largest element to be transportedstill has a substantial size, given that the rotor is a single piece. Inits completed form this rotor is fitted with strong permanent magnetsand needs to be covered by a nonmagnetic layer, e.g. wood or polystyreneof a certain thickness during transportation, and while the dimensionsof the rotor are smaller than the dimensions of the finished generator,it is still at maybe 5 m diameter and 1.5 m length a very substantialpiece of equipment to transport.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide agenerator as initially mentioned in such a way, that in particular thetransport of the generator to the site of erection is simplified. It isa further object of the invention to indicate a wind turbine comprisinga respective generator.

This object is inventively achieved by a direct drive or directly drivengenerator for a wind turbine comprising a stator having at least onestator element operative for the electrical power generation and a rotorpivotable around a centre axis of the generator and having at least onerotor element operative for the electrical power generation, thegenerator having an air gap between the stator element and the rotorelement, wherein the stator comprises a front and a rear ring-shapedsupporting element and stator segments being attached to the front andthe rear ring-shaped supporting elements of the stator, wherein thejunctions between the front and the rear ring-shaped supporting elementsof the stator and the stator segments are located substantially at aradius in relation to the centre axis of the generator which is smallerthan the radius of the air gap between the stator element and the rotorelement. According to the invention the stator of the generator is atleast partially segmented and comprises ring-shaped supporting elementsand stator segments. Thereby the ring-shaped supporting elements, whichare preferably ring-shaped end plates of the stator, and the statorsegments build in the assembled state the stator or the statorarrangement having a substantially hollow cylindrical shape. Thus thestator as a whole comprises a plurality of single manageable elementsand segments which single manageable elements and segments are as a ruleattached to each other in a detachable way. According to this theconnections in particular between the ring-shaped supporting elementsand the stator segments are non-destructively detachable. As aconsequence the transport of the stator in form of the ring-shapedsupporting elements and the stator segments and thus the transport ofthe whole generator is simplified, because at least the stator is ableto be transported in parts wherein each part has lesser dimensions and alower dead load than the generator in the assembled status. Inparticular the ring-shaped supporting elements, which are as a rule onepiece elements ensuring particularly a sufficient roundness, havedimensions in particular diameters, which are preferably significantlysmaller than the air gap diameter. This simplifies the transport of thering-shaped supporting elements of the stator. Also the assembly and thedisassembly of the stator and thus of the generator on the site oferection are simplified. In case of a wind turbine not the whole mountedgenerator has to be carried into the nacelle using e.g. a crane. In factthe significantly lighter single manageable parts and segments of thegenerator are able to be carried into the nacelle where the generator isable to be assembled, repaired or disassembled.

According to an embodiment of the invention the rotor of the generatorcomprises a front and a rear ring-shaped supporting element and rotorsegments being attached to the front and the rear ring-shaped supportingelements of the rotor, wherein the junctions between the front and therear ring-shaped supporting elements of the rotor and the rotor segmentsare located substantially at a radius in relation to the centre axis ofthe generator which is equal or smaller than the radius of the air gapbetween the stator element and the rotor element. Thus also the rotor ofthe generator is at least partially segmented, wherein the ring-shapedsupporting elements of the rotor are preferably ring-shaped end platesof the rotor. The ring-shaped supporting elements of the rotor and therotor segments build in the assembled state the rotor or the rotorarrangement having a substantially hollow cylindrical shape. Thus alsothe rotor as a whole comprises a plurality of single manageable elementsand segments which single manageable elements and segments are as a ruleattached to each other in a detachable way. In particular theconnections between the ring-shaped supporting elements of the rotor andthe rotor segments are non-destructively detachable. As a consequencethe transport of the generator is again simplified, because also therotor is able to be transported in parts wherein each part has lesserdimensions and a lower dead load than the generator in the assembledstatus. In particular the ring-shaped supporting elements of the rotor,which are as a rule one piece elements ensuring particularly asufficient roundness, have dimensions in particular diameters, which arepreferably significantly smaller than the air gap diameter. Thissimplifies the transport of the ring-shaped supporting elements of therotor.

In an embodiment of the invention the junctions of the stator and thejunctions of the rotor are located substantially at the same radius inrelation to the centre axis of the generator, which is advantageous inview of the assembly and disassembly of the generator. But it is alsopossible that the junctions of the stator and the junctions of the rotorare located at different radii in relation to the centre axis of thegenerator.

In an variant of the invention the stator segments and/or the rotorsegments are designed in such a way that the junctions between thering-shaped supporting elements of the stator and the stator segmentsand/or the junctions between the ring-shaped supporting elements of therotor and the rotor segments are located substantially at a radius inrelation to the centre axis of the generator which is equal or smallerthan the radius of the air gap between the stator elements and the rotorelements. Preferably the junctions are located at a radius which issmaller than the radius of the air gap. In this way the outer diametersof the ring-shaped supporting elements of the stator and the rotor areable to be significantly smaller than the diameter of the air gap of thegenerator, thereby reducing the maximum dimensions of the ring-shapedsupporting elements of the stator and the rotor in particular fortransportation. Thereby the diameters or the maximal dimensions of thering-shaped supporting elements of the stator and the rotor can differfrom each other.

According to an embodiment of the invention each stator segment is aring-segment-shaped stator segment attached to the front and the rearring-shaped supporting element of the stator and comprises at least onestator element for the power generation. Thereby the ring-segment-shapedstator segments build a stator ring after the arrangement on thering-shaped supporting elements of the stator.

According to another embodiment of the invention each rotor segment is aring-segment-shaped rotor segment attached to the front and the rearring-shaped supporting element of the rotor and comprises at least onerotor element for the power generation. In a comparable way to thestator the ring-segment-shaped rotor segments build a rotor ring afterthe arrangement on the ring-shaped supporting elements of the rotor.

According to an variant of the invention a ring-segment-shaped statorsegment comprises an exterior, ring-segment-shaped stator supportingelement, a radially inwardly directed front ring-segment-shaped statorconnection element arranged on the front side of the exterior,ring-segment-shaped stator supporting element and a radially inwardlydirected rear ring-segment-shaped stator connection element arranged onthe rear side of the exterior, ring-segment-shaped stator supportingelement for establishing a inwardly open, substantially U-shaped,ring-segment-shaped stator segment, wherein at least one stator elementis arranged on the inside of the exterior ring-segment-shaped statorsupporting element. Thereby the expression substantially U-shaped shallalso cover other comparable forms such as V-shaped etc.

In an comparable way a ring-segment-shaped rotor segment comprises anexterior, ring-segment-shaped rotor supporting element, a radiallyinwardly directed front ring-segment-shaped rotor connection elementarranged on the front side of the exterior, ring-segment-shaped rotorsupporting element and a radially inwardly directed rearring-segment-shaped rotor connection element arranged on the rear sideof the exterior, ring-segment-shaped rotor supporting element forestablishing a inwardly open, substantially U-shaped ring-segment-shapedrotor segment, wherein at least one rotor element is arranged on theoutside of the exterior ring-segment-shaped rotor supporting element.Thereby the expression substantially U-shaped shall again also coverother comparable forms such as V-shaped etc.

In an embodiment of the invention each rotor segment is at leastpartially arranged inside a stator segment. It is also possible that twoor more rotor segments are at least partially arranged inside a statorsegment. Thereby the stator elements and the rotor elements for thepower generation are arranged oppositely to each other with anintermediate air gap.

In a further development of the invention a stator segment and at leastone rotor segment are able to be at least temporarily supported againsteach other. Preferably each stator segment comprises first supportingprojections and each rotor segment comprises second supportingprojections, wherein the first supporting projections of a first statorsegment and the second supporting projections of a corresponding firstrotor segment are able to be at least temporarily supported against eachother. Preferably each ring-segment-shaped stator connection element ofa ring-segment-shaped stator segment comprises at least one firstsupporting projection and each ring-segment-shaped rotor connectionelement of a ring-segment-shaped rotor segment comprises at least onesecond supporting projection. By means of the supporting projections arotor segment or ring-segment-shaped rotor segment is able to rest onstator segment or a ring-segment-shaped stator segment in particularwhen the generator and the segments or the ring-segment-shaped segmentsrespectively are transported, assembled or disassembled. Thereby an airgap remains between the stator elements for the power generation and therotor elements for the power generation. Since in this way the magneticcircuits concerning the stator and rotor elements for the powergeneration are closed, normally no specific protection against undesiredmagnetic pull is needed, in particular when the generator comprisespermanent magnets. Further on, since during assembly and disassembly ofthe generator a rotor segment or a ring-segment-shaped rotor segment isallowed to rest on a stator segment or a ring-segment-shaped statorsegment, any crane lift is as a rule disconnected from magnetic pull. Asa consequence the transport, assembly and disassembly are simplified.

Therefore according to a further embodiment of the invention a statorsegment and at least one rotor segment are able to build at leasttemporarily a unit, more precisely a stator/rotor segment unit.

In a further development of the invention the width of the air gapbetween a stator element and a rotor element is adjustable. Thereby thejunctions between the ring-shaped supporting elements of the stator andthe stator segments and/or the junctions between the ring-shapedsupporting elements of the rotor and the rotor segments preferablycomprise adjusting means for the adjustment of the width of the air gap.In one embodiment of the invention the adjusting means comprise at leastone shim. Thus the desired or required width of the air gap between thestator and rotor elements for the power generation can be adjusted in arelatively simple way.

According to another embodiment of the invention a stator segmentcomprises at least one winding form with a winding as a stator elementand/or a rotor segment comprises at least one permanent magnet as arotor element.

In an embodiment of the invention the stator segments and thering-shaped supporting elements of the stator and/or the rotor segmentsand the ring-shaped supporting elements of the rotor comprise axialand/or radial extending flanges for the mounting. Thereby the axialextending flanges extend preferably substantially in the directions ofthe centre axis A of the main shaft and the radial extending flangesextend preferably substantially perpendicularly in relation to thecentre axis A of the main shaft. In this way the stator and rotorsegments can be comparatively simply attached to the respectivering-shaped supporting elements.

According to a further embodiment of the invention at least one of thering-shaped supporting elements of the rotor and/or at least one of thering-shaped supporting elements of the stator comprise at least one manhole for providing access to the internals of the generator. Thus atleast one of the front or rear ring-shaped supporting elements can haveone or more man holes which are preferably closable.

The further object of the invention is inventively achieved by a windturbine comprising a generator as described afore.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be explained in more detail withreference to the schematic drawings, wherein

FIG. 1 shows a part of an inventive wind turbine,

FIG. 2 shows in an enlarged illustration the main shaft and a part ofthe direct drive generator of the wind turbine of FIG. 1,

FIG. 3 shows in an enlarged illustration a part of the direct drivegenerator of the wind turbine of FIG. 1, and

FIG. 4 shows the view of the generator of the wind turbine of FIG. 1 inthe direction of the arrows IV of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically a first embodiment of an inventive windturbine 1 comprising an inventive direct drive or directly drivengenerator 2 which is arranged on the upwind side of a tower 3 of thewind turbine 1.

A tower flange 4 is arranged on the top of the tower 3. A retainingarrangement is arranged on the tower flange 4 comprising in case of thepresent embodiment of the invention a bedplate 5, a retaining frame inform of a retaining arm 6 and a stationary or fixed hollow shaft 7. Thebedplate 5 is attached to the tower flange 4. The wind turbine 1comprises in a not explicitly shown manner a yaw system for turning thebedplate 5 of the wind turbine 1 around the centre axis Y of the tower 3together with the other components of the wind turbine 1 which aredirectly or indirectly attached to the bedplate 5.

The retaining arm 6 is on its base side directly arranged on thebedplate 5. On the other side the retaining arm 6 comprises a flange 8.The stationary shaft 7 is attached to the flange 8 with a flange 9. Thering-shaped flange 8 of the retaining arm 6 and the ring-shaped flange 9of the stationary shaft 7 are bolted together with a plurality of boltsarranged around the ring shaped flanges.

A main shaft 10 or a main rotor pipe 10 is pivoted on the stationaryshaft 7 by means of a first main bearing 11 and a second main bearing12. Each main bearing 11, 12 supported by the stationary shaft 7comprises an inner and an outer bearing shell. The inner bearing shellsof the both main bearings 11, 12 are mounted on the stationary shaft 7,whilst the outer bearing shells of the both main bearings 11, 12 arefitted inside the main shaft 10.

On the front end the main shaft 10 comprises a ring-shaped flange 13.The ring-shaped flange 13 is firmly, but detachably connected to a hub14 of the wind turbine 1. The hub 14 comprises three mounting devices 15for three not explicitly shown, but well known wind rotor blades.

In case of the present embodiment of the invention the mentioned directdrive or directly driven generator 2 is substantially arranged aroundthe main shaft 10. The direct drive generator 2 comprises a rotor 16 ora rotor arrangement 16 and a stator 17 or a stator arrangement 17.

The rotor 16 comprises in case of the present embodiment of theinvention a first supporting element 18 in form of a front ring-shapedrotor end plate 18, a second supporting element 19 in form of a rearring-shaped rotor end plate 19 and a plurality of ring-segment-shapedrotor segments 20 attached to the front ring-shaped rotor end plate 18and the rear ring-shaped rotor end plate 19. In case of the presentembodiment of the invention the rotor 16 comprises sixring-segment-shaped rotor segments 20 building a rotor ring when the sixring-segment-shaped rotor segments 20 are attached to the preferablyone-piece front and rear ring-shaped rotor end plates 18, 19.

The stator 17 comprises in case of the present embodiment of theinvention a first supporting element 26 in form of a front ring-shapedstator end plate 26, a second supporting element 27 in form of a rearring-shaped stator end plate 27 and a plurality of ring-segment-shapedstator segments 28 attached to the front ring-shaped stator end plate 26and the rear ring-shaped stator end plate 27. In case of the presentembodiment of the invention the stator 17 comprises also sixring-segment-shaped stator segments 28 (cp. FIG. 4) building a statorring when the six ring-segment-shaped stator segments 28 are attached tothe preferably one-piece front and rear ring-shaped stator end plates26, 27.

In case of the present embodiment of the invention thering-segment-shaped stator segments 28 and the ring-segment-shaped rotorsegments 20 are designed in such a way that the junctions 50, 51 betweenthe ring-shaped stator end plates 26, 27 and the ring-segment-shapedstator segments 28 as well as the junctions 52, 53 between thering-shaped rotor end plates 18, 19 and the ring-segment-shaped rotorsegments 20 are located substantially at a radius R1 in relation to acentre axis A of the generator 2 which is smaller than the radius R2 ofthe air gap 34 between stator elements 33 for the power generationarranged on the ring-segment-shaped stator segments 28 and rotorelements 25 for the power generation arranged on the ring-segment-shapedrotor segments 20. Thus in case of the present embodiment of theinvention the maximum diameters of the ring-shaped stator and rotor endplates are 2*R1. These diameters are significantly smaller than thediameter of the air gap 34 (2*R2). This simplifies the transport of thering-shaped stator and rotor end plates.

A ring-segment-shaped rotor segment 20 comprises an exterior,ring-segment-shaped rotor supporting element 54, a radially inwardlydirected front ring-segment-shaped rotor connection element 55 arrangedon the front side of the exterior, ring-segment-shaped rotor supportingelement 54 and a radially inwardly directed rear ring-segment-shapedrotor connection element 56 arranged on the rear side of the exterior,ring-segment-shaped rotor supporting element 54 for establishing aninwardly open, substantially U-shaped ring-segment-shaped rotor segment20, wherein at least one rotor element 25 in form of at least onepermanent magnet 25 is arranged on the outside of the exteriorring-segment-shaped rotor supporting element 54. Thereby aring-segment-shaped rotor segment 20 connects the front and the rearring-shaped rotor end plates 18, 19 with each other.

As shown in FIG. 2 and FIG. 3 a front ring-segment-shaped rotorconnection element 55 comprises on its end a ring-segment-shaped flange21 and a ring-segment-shaped supporting projection 57. A rearring-segment-shaped rotor connection element 56 comprises on its end aring-segment-shaped flange 22 and a ring-segment-shaped supportingprojection 58. The front ring-shaped rotor end plate 18 has aring-shaped flange 23 and the rear ring-shaped rotor end plate 19 has aring-shaped flange 24. In case of the present embodiment of theinvention the flanges 21 and 23 as well as the flanges 22 and 24 arebolted together to build up the rotor 16. In the described way allring-segment-shaped rotor segments 20 are attached to the front and therear ring-shaped end plates 18, 19. Thus the rotor 16 has substantiallya hollow-cylindrical shape.

In a comparable way a ring-segment-shaped stator segment 28 comprises anexterior, ring-segment-shaped stator supporting element 67, a radiallyinwardly directed front ring-segment-shaped stator connection element 68arranged on the front side of the exterior, ring-segment-shaped statorsupporting element 67 and a radially inwardly directed rearring-segment-shaped stator connection element 69 arranged on the rearside of the exterior, ring-segment-shaped stator supporting element 67for establishing an inwardly open, substantially U-shaped,ring-segment-shaped stator segment, wherein at least one stator element33 in form of a winding form 75 with a winding 76 is arranged on theinside of the exterior ring-segment-shaped stator supporting element 67.Thereby a ring-segment-shaped stator segment 28 connects the front andthe rear ring-shaped stator end plates 26, 27 with each other.

As shown in FIG. 2 and FIG. 3 a front ring-segment-shaped statorconnection element 68 comprises on its end a ring-segment-shaped flange29 and a ring-segment-shaped supporting projection 60. A rearring-segment-shaped stator connection element 69 comprises on its end aring-segment-shaped flange 30 and a ring-segment-shaped supportingprojection 61. The front ring-shaped stator end plate 26 has aring-shaped flange 31 and the rear ring-shaped stator end plate 27 has aring-shaped flange 32. In case of the present embodiment of theinvention the flanges 29 and 31 as well as the flanges 30 and 32 arebolted together to build up the stator 17. In the described way allring-segment-shaped stator segments 28 are attached to the front and therear ring-shaped stator end plates 26, 27. Thus also the stator 17 hassubstantially a hollow-cylindrical shape.

In case of the present embodiment of the invention eachring-segment-shaped rotor segment 20 is substantially arranged inside aring-segment-shaped stator segment 28. In particular during thetransport, the assembly and the disassembly of the ring-segment-shapedstator and rotor segments 20, 28 one ring-segment-shaped stator segment28 and one ring-segment-shaped rotor segment 20 are able to build astator/rotor segment unit. Thereby the ring-segment-shaped rotor segment20 is moved into the ring-segment-shaped stator segment 28 until thering-segment-shaped rotor segment 20 rests on the ring-segment-shapedstator segment 28. More precisely the projections 57, 58, 60, 61 engage,whereat the supporting projection 60 and the supporting projection 57 aswell as the supporting projection 61 and the supporting projection 58are supported against each other. In general the projections 57, 58, 60,61 engage if the air gap between the stator elements and the rotorelements for the power generation is reduced to a value a certain levelbelow the nominal value of the air gap. The magnetic pull during themounting of the stator/rotor segment unit is counteracted by suitabletools, e.g. a set of jacks. Once the projections 57, 58, 60, 61 engage,the magnetic pull is taken by the projections and the suitable tools canbe removed. In this position the magnetic circuits are as a rule closedand the stator/rotor segment unit no longer poses any risk in relationto the strong permanent magnets. The stator/rotor segment unit is ableto be transported, assembled and disassembled with no specialprecautions.

On the site of erection of the wind turbine 1 first the supportingstructures are assembled—the stationary shaft 7, the main bearings 11,12, the main shaft 10, a third and a fourth bearing 35, 36, describedlater, and the ring-shaped rotor end plates 18, 19 as well as thering-shaped stator end plates 26, 27.

For the assembly of the generator 2 a stator/rotor segment unit is, asindicated above, arranged on the front and the rear ring-shaped endplates 18, 19, 26, 27. Thereby the flange 29 of a frontring-segment-shaped stator connection element 68 and the flange 31 ofthe front ring-shaped stator end plate 26 as well as the flange 30 of arear ring-segment-shaped stator connection element 69 and the flange 32of the rear ring-shaped stator end plate 27 are bolted together withschematically shown flange bolts 62. This is done for all sixstator/rotor segment units. Any necessary adjustment of the radialposition of a ring-segment-shaped stator segment 28 is carried out withnot explicitly shown shims in the junctions 50, 51 between the flanges29, 31 as well as between the flanges 30, 32. Thereby the respectiveshims are inserted between the respective flanges and then the flangebolts 62 are inserted in respective bolt holes and tightened.

Afterwards the flanges 21 of the front ring-segment-shaped rotorconnection elements 55 and the flange 23 of the front ring-shaped rotorend plate 18 and the flanges 22 of the rear ring-segment-shaped rotorconnection elements 56 and the flange 24 of the rear ring-shaped rotorend plate 19 are bolted together with schematically shown flange bolts63. Thereby the ring-segment-shaped rotor segments 20 are as a rulepulled away from the resting position, in which the projections 57, 58,50, 61 engage. Any necessary adjustment of the radial position of aring-segment-shaped rotor segment 20 is carried out with not explicitlyshown shims in the junctions 52, 53 between the flanges 21, 23 as wellas between the flanges 22, 24 before the flange bolts 63 are inserted inrespective bolt holes and finally tightened.

If a ring-segment-shaped rotor segment 20 or a ring-segment-shapedstator segment 28 needs e.g. replacement the described steps are carriedout in reverse order and the replacement stator/rotor segment unit isassembled as described.

Based on trial rotations the radial positions of the ring-segment-shapedrotor segments 20 as well as the radial positions of thering-segment-shaped stator segments 28 are able to be fine tuned withthe shims in the junctions 50-53. Thus the width of the air gap 34between the electrical stator elements 33 of the stator 17 and thepermanent magnets 25 of the rotor 16 is able to be adjusted to establisha preferably completely uniform and concentric air gap 34.

In order that the rotor 16 can turn together with the main shaft 10around the centre axis A of the main shaft 10 and relatively to thestator 17 the wind turbine 1 in particular the direct drive generator 2comprise the already mentioned third or front generator bearing 35 andthe already mentioned fourth or rear generator bearing 36. The relativepositions of the stator 17 and the rotor 16 are maintained by the thirdand the fourth bearing 35, 36.

The third bearing 35 is in case of the present embodiment of theinvention attached to a flange 37 of the main shaft 10. More preciselythe inner bearing shell 38 of the third bearing 35 is firmly attached tothe flange 37 of the main shaft 10. The inner bearing shell 38 of thethird bearing 35 is furthermore firmly attached to the front ring-shapedrotor end plate 18, which supports the front part of the rotor 16. Theouter bearing shell 39 of the third bearing 35 is firmly connected tothe front ring-shaped stator end plate 26, which supports the front partof the stator 17.

The rear part of the stator 17 is supported by the rear ring-shapedstator end plate 27, which is firmly connected to the flange 9 of thestationary shaft 7 and thus to the retaining arrangement. In case of thepresent embodiment of the invention the inner bearing shell 40 of thefourth bearing 36 is firmly attached to the rear ring-shaped stator endplate 27 and the rear ring-shaped rotor end plate 19 supporting the rearpart of the rotor 16 is firmly connected to the outer bearing shell 41of the fourth bearing 36.

Based on the described arrangement comprising the main shaft 10, thefirst main bearing 11, the second main bearing 12, the rotor 16, thestator 17, the third bearing 35 and the fourth bearing 36 the main shaft10 turns in operation of the wind turbine 1 together with the rotor 16relatively to the stator 17.

For avoiding situations in which the four bearing arrangement isstatically undetermined in case of the present embodiment of theinvention the front ring-shaped rotor end plate 18 firmly supported onthe main shaft 10 and the rear ring-shaped stator end plate 27 firmlysupported on the retaining arrangement comprise a certain and sufficientextent of flexibility in the directions of the centre axis A of the mainshaft 10. Thereby these end plates 18, 27 act like membranes supportingthe rotor 16 and the stator 17 substantially firmly in the radialdirection so as to maintain the width of the air gap 34, but flexingreadily so as to allow e.g. a bending of the main shaft 10 with no majorresistance. In particular the end plates 18, 27 have such dimensionsthat they have a comparatively little bending stiffness. They simplyflex passively when e.g. the main shaft 10 is shifted a bit bydeflection. Thus when a bending of the main shaft 10 occurs to which therotor 16 and the stator 17 are connected the front ring-shaped rotor endplate 18 and the rear ring-shaped stator end plate 27 bend insubstantially a respective way in the directions of the centre axis Awherein the width of the air gap 34 is maintained substantially constantor within required tolerances.

As a consequence of the four bearing arrangement, in addition to theloads from the wind turbine rotor and the main shaft 10 the two mainbearings 11, 12 carry approximately half of the weight of the generator2, approximately the other half of the weight of the generator 2 isdirectly supported on the retaining arrangement. The third or frontgenerator bearing 35 carries approximately half of the weight of thestator 17, approximately the other half of the weight of the stator 17is supported on the retaining arrangement. The fourth or rear generatorbearing 36 carries approximately half of the weight of the rotor 16,approximately the other half of the weight of the rotor 16 is supportedon the main shaft 10.

Based on the described design or structure of the wind turbine 1 inparticular based on the described generator arrangement comprising thethird and fourth bearing the rotor 16 and the stator 17 are supported onboth sides, the front side and the rear side. This enables a morelightweight rotor and in particular a more lightweight statorconstruction with less dimensions of the stator structure in particularof the stator support structure like the end plates and so on tomaintain in operation of the wind turbine 1 the width of the air gap 34within the necessary tolerances along the directions of the centre axisA and around the perimeter.

Unlike to the afore described embodiment of the invention the frontring-shaped stator end plate 26 and the rear ring-shaped rotor end plate19 are able to comprise the certain extent of flexibility in thedirections of the centre axis A of the main shaft 10, whilst the frontring-shaped rotor end plate 18 and the rear ring-shaped stator end plate27 have not these flexibility. Also in this case the width of the airgap 34 is able to be held substantially constantly or at least withinrequired tolerances.

The ring-shaped rotor end plate and the ring-shaped stator end platewhich have the certain flexibility need not to have the flexibility inthe whole end plates. Thus the ring-shaped end plates are able to havedifferent areas. The respective ring-shaped rotor end plate may havee.g. a comparatively rigid area e.g. for the attachment of the thirdbearing and an area having the mentioned flexibility in the directionsof the centre axis A. In the same way the respective ring-shaped statorend plate may have e.g. a comparatively rigid area e.g. for theattachment of the fourth bearing and an area having the mentionedflexibility in the directions of the centre axis A.

The front ring-shaped rotor end plate is able to be directly arranged onthe main shaft. In this case the third bearing is able to be directlyattached to the main shaft or to the front ring-shaped rotor end plate.

It is not necessary to attach the fourth bearing to the rear ring-shapedstator end plate. The fourth bearing is also able to be directlyattached to the retaining arrangement e.g. the stationary shaft or theretaining frame or arm.

As a rule the ring-shaped end plates are made of an appropriate metal ormetal alloy. The ring-shaped end plates do not need to have the samediameter. In fact the different ring-shaped end plates are able to havedifferent diameters. In this case also the respectivering-segment-shaped segments have to be modified in relation to theradial extension of the radially inwardly directed ring-segment-shapedstator connection elements to build the stator or the rotor.

FIG. 4 shows the view of the generator 2 of the wind turbine 1 in thedirection of the arrows IV of FIG. 1. In FIG. 4 the third or generatorbearing 35, the front ring-shaped stator end plate 26, the flanges 29,31 and the six ring-segment-shaped stator segments 28 building thestator ring 71 are cognizable. In case of the present embodiment of theinvention the front ring-shaped stator end plate 26 comprises six manholes 70 providing access to the internals of the generator. In the sameway the other ring-shaped end plates of the stator or the rotor are ableto comprise man holes. Thereby the man holes are as a rule closed bymeans of a kind of door.

In case of the present embodiment of the invention in eachring-segment-shaped stator segment 28 a ring-segment-shaped rotorsegment 20 is substantially centrically arranged. But it is alsopossible that two or more ring-segment-shaped rotor segments 20 aresubstantially arranged in a ring-segment-shaped stator segment 28.

By the way the generator 2 is able to comprise less or morering-segment-shaped stator segment 28 building the stator ring as wellas less or more ring-segment-shaped rotor segment 20 building the rotorring as described afore. Furthermore it is not necessary that the rotorsegments or the stator segments have a ring-segment shape.

The non-destructively detachable connections between the end plates andthe ring-segment-shaped segments need not to be a bolted joint.

In case of the described embodiment of the invention thering-segment-shaped stator segments 28 and the ring-shaped stator endplates 26, 27 as well as the ring-segment-shaped rotor segments 20 andthe ring-shaped rotor end plates 18, 19 comprise axial extending flanges21-24, 29-32 for the mounting. Thereby the axial extending flanges21-24, 29-32 extend substantially in the directions of the centre axisA. But the mounting is also able to be done by radial extending flangesor other suitable means. Thereby the radial extending flanges extendsubstantially perpendicularly in relation to the centre axis A.

Unlike described before the direct drive generator is also able to bearranged on the downwind side of the tower.

By the way the wind turbines 1 comprise a housing H normally called thenacelle which contain the generator 2 and at least a part of theretaining arrangement.

1-20. (canceled)
 21. A direct drive generator for a wind turbine, comprising: a stator; a stator element comprised in the stator for generating a power; a front ring-shaped supporting element of the stator; a rear ring-shaped supporting element of the stator; a stator segment attached to the front and the rear ring-shaped supporting elements of the stator; a rotor pivotable around a centre axis of the generator; a rotor element comprised in the rotor for generating the power; and a junction of the stator between the front and the rear ring-shaped supporting elements of the stator and the stator segment that is located substantially at a radius in relation to the centre axis of the generator and is smaller than a radius of an air gap between the stator element and the rotor element.
 22. The generator as claimed in claim 21, wherein the rotor comprises: a front ring-shaped supporting element of the rotor, a rear ring-shaped supporting element of the rotor, a rotor segment being attached to the front and the rear ring-shaped supporting elements of the rotor, and a junction of the rotor between the front and the rear ring-shaped supporting elements of the rotor and the rotor segment that is located substantially at the radius in relation to the centre axis of the generator and is equal or smaller than the radius of the air gap between the stator element and the rotor element.
 23. The generator as claimed in claim 22, wherein the junction of the stator and the junction of the rotor are located substantially at the same radius in relation to the centre axis of the generator.
 24. The generator as claimed in claim 22, wherein the stator segment or the rotor segment is designed so that the junction of the stator or the junction of the rotor is located substantially at the radius in relation to the centre axis of the generator which is equal or smaller than the radius of the air gap between the stator element and the rotor element.
 25. The generator as claimed in claim 22, wherein the rotor segment is at least partially arranged inside of the stator segment.
 26. The generator as claimed in claim 22, wherein the stator segment and the rotor segment are at least temporarily supported against each other.
 27. The generator as claimed in claim 22, wherein the rotor segment is a ring-segment-shaped rotor segment attached to the front and the rear ring-shaped supporting elements of the rotor and comprises the rotor element for generating the power.
 28. The generator as claimed in claim 27, wherein the ring-segment-shaped rotor segment is inwardly open and comprises: an exterior ring-segment-shaped rotor supporting element, a radially inwardly directed front ring-segment-shaped rotor connection element arranged on a front side of the exterior ring-segment-shaped rotor supporting element, and a radially inwardly directed rear ring-segment-shaped rotor connection element arranged on a rear side of the exterior ring-segment-shaped rotor supporting element, wherein the rotor element is arranged on an outside of the exterior ring-segment-shaped rotor supporting element.
 29. The generator as claimed in claim 28, wherein the stator segment is a ring-segment-shaped stator segment attached to the front and the rear ring-shaped supporting elements of the stator and comprises the stator element for generating the power.
 30. The generator as claimed in claim 29, wherein the ring-segment-shaped stator segment is inwardly open and comprises: an exterior ring-segment-shaped stator supporting element, a radially inwardly directed front ring-segment-shaped stator connection element arranged on a front side of the exterior ring-segment-shaped stator supporting element, and a radially inwardly directed rear ring-segment-shaped stator connection element arranged on a rear side of the exterior ring-segment-shaped stator supporting element, wherein the stator element is arranged on an inside of the exterior ring-segment-shaped stator supporting element.
 31. The generator as claimed in claim 30, wherein the stator segment comprises a first supporting projection, wherein the rotor segment comprises a second supporting projection, and wherein the first supporting projection and the second supporting projection are at least temporarily supported against each other.
 32. The generator as claimed in claim 31, wherein the front and the rear ring-segment-shaped stator connection elements comprise the first supporting projection, and wherein the front and the rear ring-segment-shaped rotor connection elements comprise the second supporting projection.
 33. The generator as claimed in claim 22, wherein the stator segment and the rotor segment build at least temporarily a stator/rotor segment unit.
 34. The generator as claimed in claim 22, wherein a width of the air gap between the stator element and the rotor element is adjustable.
 35. The generator as claimed in claim 34, wherein the junction of the stator or the junction of the rotor comprises an adjusting device for adjusting the width of the air gap.
 36. The generator as claimed in claim 35, wherein the adjusting device comprises a shim.
 37. The generator as claimed in claim 22, wherein the stator segment comprises a winding form with a winding which is used as the stator element, and wherein the rotor segment comprises a permanent magnet which is used as the rotor element.
 38. The generator as claimed in claim 22, wherein the stator segment and the front and the rear ring-shaped supporting elements of the stator or the rotor segment and the front and the rear ring-shaped supporting elements of the rotor comprise an axial or a radial extending flange for mounting.
 39. The generator as claimed in claim 22, wherein the front and the rear ring-shaped supporting elements of the stator or the front and the rear ring-shaped supporting elements of the rotor comprises a man hole for accessing to an internal of the generator.
 40. A wind turbine, comprising: a generator that comprises: a stator; a stator element comprised in the stator for generating a power; a front ring-shaped supporting element of the stator; a rear ring-shaped supporting element of the stator; a stator segment attached to the front and the rear ring-shaped supporting elements of the stator; a rotor pivotable around a centre axis of the generator; a rotor element comprised in the rotor for generating the power; and a junction of the stator between the front and the rear ring-shaped supporting elements of the stator and the stator segment that is located substantially at a radius in relation to the centre axis of the generator and is smaller than a radius of an air gap between the stator element and the rotor element. 